A magnetic disk device uses a magnetic head to read and write data out of and from a recording medium. In order to increase a recording capacity of a magnetic disk per unit area, it is necessary to increase a surface recording density. In a current in-plane recording scheme, however, when a bit length to be recorded is reduced, the surface recording density cannot be increased due to heat fluctuation caused by magnetization in the recording medium. To solve the problem, there is a perpendicular recording scheme for recording a magnetization signal in a direction perpendicular to the surface of the recording medium. In the perpendicular recording scheme, in order to read data, a giant magnetoresistance effect (GMR) head, a tunnel magnetoresistance effect (TMR) head capable of providing a large reproduction output, and a current perpendicular to plane (CPP) GMR head capable of causing a current to flow perpendicularly to a film surface, are used. On the other hand, in order to write data, a single magnetic pole head is used.
In the perpendicular recording scheme, in order to increase the surface recording density, it is necessary to increase a track density and a linear recording density. In order to increase the track density and the linear recording density, it is necessary to prevent a fringe magnetic field from being generated from a main magnetic pole of the single magnetic pole head and cause the gradient of a magnetic field to be steep. To prevent the fringe magnetic field and cause the gradient of the magnetic field to be steep, it is effective to arrange a magnetic shield on a trailing side of the main magnetic pole and on both sides of the main magnetic pole. When the magnetic shield is arranged around the main magnetic pole, the intensity of the magnetic field generated from the main magnetic pole is reduced. It is therefore necessary to increase a current flowing in a coil. In order to increase the linear recording density, the frequency of a recording signal is high. When a magnetic path length of a magnetic circuit is large, a high frequency property is reduced. Thus, the width of a conductive coil layer is reduced, or the number of winding turns of the coil is reduced, to reduce the magnetic path length. Instead, a current flowing in the coil is increased. However, resistance of a coil of a thin film magnetic head is relatively high. When the width of the coil is reduced, the resistance of the coil is increased. An effect of heat generated from the coil due to the increase in the current is significant. That is, a portion present near a read/write element may protrude due to heat expansion caused by the heat generated from the coil and contact the magnetic disk.
To solve the problem, Japanese Patent Application No. 5-159234 discloses a thin film head assembly, for example. The thin film head assembly includes a coil structure having a thin coil layer and an additional coil layer. The thin coil layer extends through a magnetic yoke region having a contour between pole pieces facing each other. The additional coil layer is adjacent to the thin coil layer and formed as a stepwise segment. The additional coil layer is separated from the pole pieces and the magnetic yoke region, and constitutes a coil region having a large thickness to cause a reduction in the resistance of the coil.
In order to maintain a high efficiency by means of the thin film magnetic head including the perpendicular magnetic recording head, it is necessary to significantly reduce a coil pitch. This results in an increase in the resistance of the coil. In order to reduce the resistance of the entire coil of the thin film magnetic head, it is considered that the width of the coil is increased. However, the coil having a large width requires an excessively large yoke structure. This reduces an efficiency of a converter and a high frequency property. As another method, the thickness of the entire coil is increased. This method may cause halation in a process of exposing a photoresist. Therefore, the thickness of the entire coil is limited.
In order to maintain a high efficiency by means of a thin film magnetic head including a perpendicular magnetic recording head, it is necessary to significantly reduce a coil pitch. This results in an increase in resistance of the coil. When the resistance of the coil is increased, a portion present near a read/write element may protrude due to heat expansion caused by heat generated from the coil.